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Publication numberUS5835284 A
Publication typeGrant
Application numberUS 08/882,939
Publication dateNov 10, 1998
Filing dateJun 26, 1997
Priority dateJun 28, 1996
Fee statusPaid
Publication number08882939, 882939, US 5835284 A, US 5835284A, US-A-5835284, US5835284 A, US5835284A
InventorsTetsuo Takahashi, Yasuhiro Omura
Original AssigneeNikon Corporation
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Catadioptric optical system and adjusting method
US 5835284 A
Abstract
A catadioptric optical system in which a first imaging optical system is constructed of a unidirectional optical apparatus which transmits outgoing light from a first plane in one direction only and a bidirectional optical apparatus for transmitting the light that enters and reflecting the same to form an interim image of the first plane. A light guide guides the light from the interim image to a second imaging optical system through which the interim image is reimaged on a second plane. The unidirectional optical apparatus has an optical axis and at least one lens movable along the optical axis.
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Claims(8)
What is claimed is:
1. A catadioptric optical system comprising:
a first plane;
a first imaging optical system having
an unidirectional optical apparatus with an optical axis and at least one lens movable with respect to said optical axis, said unidirectional optical apparatus being arranged to receive light from said first plane and for transmitting said light in only a first direction; and
a bidirectional optical apparatus for receiving said transmitted light and for reflecting said light to form an interim image of said first plane;
a second plane;
a second imaging optical system for receiving light from said interim image and reimaging said interim image on said second plane; and
a light guide for guiding light from said interim image to said second imaging optical system.
2. A system, as claimed in claim 1, wherein said bidirectional optical apparatus includes a concave mirror and a lens group which transmits both incident light and reflected light with respect to said concave mirror.
3. A system, as claimed in claim 1, wherein said light guide is a mirror.
4. A system, as claimed in claim 1, wherein said lens is movable along said optical axis.
5. A system, as claimed in claim 1, wherein said lens is movable in a direction perpendicular to said optical axis.
6. A system, as claimed in claim 1, wherein said lens is rotatable about an axis perpendicular to said optical axis.
7. A method of adjusting the catadioptric optical system of claim 1, comprising the steps of:
arranging a test pattern on said first plane;
detecting a partial imaging position of said test pattern on said second plane by means of a position detector;
moving said position detector through a plurality of positions to detect a plurality of partial imaging positions of said test pattern on said second plane; and
moving at least said lens to a position based on said plurality of partial imaging positions.
8. A system, as claimed in claim 1, wherein a reticle having a circuit pattern is arranged in said first plane and a wafer having a photosensitive substrate is placed in said second plane.
Description
BACKGROUND OF THE INVENTION

The present invention relates to a catadioptric optical system and a method for adjusting the system. More particularly, the present invention relates to a system in which a pattern on an object in a first plane is superimposingly photo-printed first as an interim image and then onto an object in a second plane, and to a method of adjusting such optical system.

A catadioptric optical system (U.S. Pat. No. 4,779,966) has been proposed for correcting curvature of field and magnification chromatic aberration in a projection exposure apparatus used in lithographic processing during the manufacturing of semiconductor devices and the like.

In a projection exposure apparatus having a catadioptric optical system, the aberration in the projection optical system is substantially measured during assembly of optical members for the projection optical system. Micro adjustments are performed using the following methods: adjusting the distances between the optical members by varying the thickness of the washer arranged between lens cylinders which hold each of the optical members; tilting the optical members (rotating them around the axis perpendicular to the optical path); and shifting the optical members (in the direction perpendicular to the optical axis). These adjustments minimize the deterioration of optical function which is normally caused during assembly of the optical members.

Further, a magnification correction optical system has been proposed (Kokai H6-331932) for the catadioptric optical system which is relatively close to unit magnification.

However, the above-mentioned optimal aberration correction system has not been established for a catadioptric optical system for reduction with a relatively large exposure area and a large numerical aperture (N.A.)

SUMMARY OF THE INVENTION

It is accordingly an object of the present invention to overcome the problems developed in prior art solutions.

It is a further object of the present invention to correct each optical aberration in a catadioptric optical system by positioning the aberration correction system at an optimal location for easy correction.

In order to achieve the above objectives, the apparatus incorporating the principles of the present invention provides a catadioptric optical system in which:

a first imaging optical system has a unidirectional optical apparatus which transmits outgoing light from a first plane only, and a bidirectional optical apparatus arranged to receive light transmitted by the unidirectional apparatus and to reflect such light to form an interim image of the first plane;

a light guide is arranged to guide the light from the interim image to a second imaging optical system through which the interim image is reimaged on a second plane. The unidirectional optical apparatus has an optical axis and at least one lens which is movable with the respect to the optical axis thereof. In an embodiment of the present invention, the lens is movable along the optical axis.

In another embodiment, the lens is movable in a direction perpendicular to the optical axis.

In a further embodiment, the lens is rotatable about an axis perpendicular to the optical axis.

In a preferred embodiment of the present invention, the bidirectional optical apparatus includes a concave mirror and a lens group which transmits both incident light and reflected light with respect to the concave mirror.

In general, the coefficient of aberrations which are symmetric around the optical path is expressed in the following equation (1): ##EQU1## where N is a coefficient of the total optical system aberration for each aberration, Ni is a coefficient of the aberration at each lens surface i for each aberration, and k is the total number of lens surfaces i along the optical axis. Each surface of the lenses in the bidirectional optical system contributes twice to each of the aberration coefficients Ni. Therefore, it is difficult to correct independently the axially symmetrical aberrations using each lens surface in the bidirectional optical apparatus. The apparatus incorporating the principles of the present invention, however, provides various aberration correction mechanisms in the unidirectional optical apparatus to provide easy correction of the axially symmetrical aberrations.

The coefficient of eccentric aberrations which are asymmetric around the optical path is only affected by the coefficient of the aberrations which are produced, when one element is shifted or tilted, by the shifted or tilted element or the elements behind it. In the reflective-refractive optical system in which the exposure area is relatively large and the N.A. is large, in general, the aberrations at the interim imaging position, where higher aberrations are easily developed, in particular are not completely corrected. For this reason, even if an adjustment mechanism that uses eccentricity is arranged near the interim image, it is easy to generate higher aberrations and difficult to correct the eccentric aberrations. However, when paying attention to an entire reflective-refractive optical system, it is possible to design a system in which the aberration is substantially corrected.

If, besides correcting the total aberration in the entire reflective-refractive optical system as much as possible in advance, eccentric aberration correction mechanisms are provided in the unidirectional optical apparatus, eccentric aberrations are produced only by the eccentric aberrations generated in the aberration correction mechanisms. This is because the unidirectional optical apparatus is arranged as the last row of lenses when the relationship between the object and the image is reversed going down the optical path backward. In addition, when the eccentric aberration correction mechanisms are provided in the unidirectional optical apparatus, the aberrations are corrected with a small number of elements. For this reason, a higher aberration coefficient rarely occurs.

In the apparatus incorporating the principles of the present invention, as described above, various aberration correction mechanisms are provided in the unidirectional optical apparatus of the first imaging optical system. By adjusting these aberration correction mechanisms, both axially symmetric aberrations and eccentric aberrations can be easily corrected.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features, and advantages of the present invention will become more apparent from the following detailed description taken with the accompanying drawings, in which:

FIG. 1 is a schematic drawing showing the construction of an embodiment of the present invention;

FIG. 2 is a schematic configuration of an aberration measurement apparatus used for an aberration adjustment method in accordance with the principles of the present invention;

FIG. 3 is a plan view of a test pattern used with the apparatus of FIG. 2;

FIG. 4 is a plan view showing an aperture plate;

FIG. 5 is a plan view showing the image of one mark of the test pattern of FIG. 3 and the aperture plate of FIG. 4;

FIG. 6 is a graphical waveform showing the measuring method of the x coordinate of the mark of FIG. 5; and

FIG. 7 is a graphical waveform showing the measuring method of the y coordinate of the mark of FIG. 5.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to the drawings, and more particularly to FIG. 1, an embodiment of the present invention is illustrated. This reflective-refractive optical system is applied to a projection optical system in which a circuit pattern on a reticle R in a first plane is reduced and transferred onto a photosensitive surface of a semiconductor wafer W in a second plane. This projection optical system is constructed with a first imaging optical system A, in which an interim image of the pattern on the reticle R is formed. The system further includes a first mirror M1 arranged in the vicinity of the interim image, and a second imaging optical system B, in which the interim image is reimaged on the wafer W.

The first imaging optical system A is constructed of a unidirectional optical apparatus A1 having an optical axis perpendicular to the first plane containing the reticle R and which transmits outgoing light from the reticle R in one direction only, and a bidirectional optical apparatus A2 which transmits the light from the unidirectional optical path A1 in two directions. In the bidirectional optical system A2, a concave mirror Mc is provided so as to reflect the light incident thereon from the unidirectional optical apparatus A1. The lens closest to the concave mirror Mc is a concave lens. The light passing through the bidirectional optical apparatus on its return path is guided to the second imaging optical system B by the first mirror M1. An aperture stop S is provided in the second imaging optical system B, and a second mirror M2 is arranged in the optical path before the aperture stop S.

The exposure range of the reflective-refractive optical system is in a slit or arc shape so that the optical path is confined to such slit or arc shape. By synchronously scanning the reticle R and the wafer W, a large exposure area on the wafer W can be obtained.

Table 1 below shows the parameters of the optical members of this embodiment. In this table, the first column represents the number of the optical surface as counted from the reticle R. The second column, r, represents the radius of curvature for each optical surface. The third column, d, represents the distance between adjacent optical surfaces. The fourth column represents the material of each lens, and the fifth column represents the group number of each optical member. In the fifth column, the asterisk mark (*) represents the light traveling along the return path. Note that the following shows the refractive indices, n, of fused quartz (SiO2) and fluorite (CaF2) with respect to the standard wavelength used (193 nm).

SiO2 : n=1.56019

CaF2 : n=1.50138

              TABLE 1______________________________________r           d______________________________________0    --         60.000  Reticle R1    -210.000   18.000  SiO2    A1                                     L12    -233.058   1.7343    301.818    32.109  CaF2    A1                                     L24    -415.393   19.4495    154862.242 15.248  SiO2    A1                                     L36    -528.109   5.4607    -316.309   18.000  SiO2    A1                                     L48    275.570    74.0649    342.313    48.000  CaF2    A210   -248.024   1.80611   -250.000   20.000  SiO2    A212   3438.110   286.84913   390.013    40.000  CaF2    A214   -2017.162  22.84915   421.041    20.000  SiO2    A216   230.317    47.91617   -222.542   20.000  SiO2    A218   988.626    7.27019   -11949.023 27.617  CaF2    A220   -328.913   0.50021   365.306    42.285  SiO2    A222   -1713.365  160.14423   -283.704   30.000  SiO2    A224   1076.349   30.70125   -353.136   30.701  Concave mirror Mc                                A226   1076.349   30.000  SiO2    A2 *27   -283.704   160.14428   -1713.365  42.285  SiO2    A2 *29   365.306    0.50030   -328.913   27.617  CaF2    A2 *31   -11949.023 7.27032   988.62.6   20.000  SiO2    A2 *33   -222.542   47.91634   230.317    20.000  SiO2    A2 *35   421.041    22.84936   -2017.162  40.000  CaF2    A2 *37   390.013    286.84938   3438.110   20.000  SiO2    A2 *39   -250.000   1.80640   -248.024   48.000  CaF2    A2 *41   342.313    4.06442   ∞    180.000 First mirror M143   506.214    34.041  CaF2    B44   -256.332   3.01745   -250.000   20.000  SiO2    B46   -1453.242  422.96647   ∞    150.000 Second mirror M248   -285.380   30.000  SiO2    B49   -954.824   50.00050   --         78.332  Aperture Stop S51   -220.000   45.000  CaF2    B52   -2665.536  6.53553   -200.000   27.411  SiO2    B54   -516.467   18.84455   632.373    30.000  SiO2    B56   -1060.585  19.11257   -553.788   45.000  SiO2    B58   5823.302   0.50059   -153.299   45.000  SiO2    B60   -120.000   1.24361   -125.615   66.000  SiO2    B62   3036.218   17.00063   --                 Wafer W______________________________________

The unidirectional optical apparatus A1 comprises, in sequence from the reticle R side, a meniscus lens L1 whose concave surface faces the reticle R, a first biconvex lens L2, a second biconvex lens L3, and a biconcave lens L4. Each of these lenses has an aberration correction mechanism attached. In other words, the lenses L1, L2, and L3 are arranged integrally movable along the optical axis which extends perpendicular to the reticle R. The lens L1 is also independently movable along the optical axis.

The lenses L1, L2, L3, and L4 are also arranged integrally rotatable around an axis perpendicular to the optical axis. The lenses L1, L2, and L3 are also integrally rotatable around an axis perpendicular to the optical axis; and further, the lens L1 is independently rotatable around an axis perpendicular to the optical axis.

Table 2 below shows the changes in the maximum image height Y10 and astigmatism Δm-s when the lens L1 is independently moved along the optical axis and when the lenses L1, L2, and L3 are integrally moved.

              TABLE 2______________________________________Amount of displacement in theoptical axial direction: -100  10-3         Y10               Δm-s         (10-3)               (10-3)______________________________________L1         0.392   0.087L1, L2, L3           -4.141  -0.228______________________________________

If the maximum image height Y10 after construction of the optical system is taller by y than the value of the real object, and the astigmatism is generated by Δ, the following simultaneous equations (2) and (3) are to be satisfied in order to maximize the image height and to make the astigmatism Δm-s zero by integrally shifting the lenses L1, L2, and L3 along the optical axis:

0.392/(-100)z1 -4.141/(-100)z1-3 =-y (2)

0.087/(-100)z1-3 -0.228/(-100)z1-3 =-Δ(3)

By solving the above simultaneous equations, the amount of displacement z1, and z1-3 can be obtained, the maximum image height Y10 is made to be the original value, and the astigmatism Δm-s to be zero.

Table 3 below shows the changes in m-dis (deviation of the imaging point of the maximum image height in a plane which includes the optical axis and is perpendicular to the rotation axis), s-dis (deviation of the image point of the maximum image height in a plane which includes both the optical axis and the rotation axis), and astigmatism δm-s, which is optical-axially asymmetric, for each of the following conditions: when the lens L1 is independently rotated; when the lenses L1, L2, and L3 are integrally rotated; and when the lenses L1, L2, L3, and L4 are integrally rotated. In the same table, the position of the rotation axis is the distance measured from the reticle R.

              TABLE 3______________________________________Angle of Rotation: 36   Position of   Rotation Axis             m-dis             δm-s   (1) (10-3)             (10-3)                      s-dis    (10-3)______________________________________L1   104         0.1094   -0.0324                                 -0.0020L1, L2, L3     178         0.2246   -0.0726                                 -0.5524L1, L2, L3, L4     198         0.0015   -0.0269                                 -0.2638______________________________________

If m-dis, s-dis, and asymmetric astigmatism, after constructing the optical system, respectively have the values, m, s, and δ, the following simultaneous equations (4), (5), and (6) are to be satisfied in order to make m-dis, s-dis, and asymmetric astigmatism δm-s equal zero by rotating the lens L1 by θ1, integrally rotating the lenses L1, L2, and L3 by θ1-3, and integrally rotating the lenses L1, L2, L3, and L4 by θ1-4 :

0.1094/36θ1 +0.2246/36θ1-3 +0.0015/36θ1-4 =-m                   (4)

-0.0324/36θ1 -0.0726/36θ1-3 -0.0269/36θ1-4 =-s                   (5)

-0.002/36θ1 -0.5524/36θ1-3 -0.2638/36θ1-4 =-δ             (6)

By solving the above simultaneous equations, the angles of rotation θ1, θ1-3, and θ1-4 can be obtained, and accordingly m-dis, s-dis, and asymmetric astigmatism δm-s can be made to equal zero.

According to this embodiment, as described above, of optical-axially symmetric components, the magnification and astigmatism aberrations can be corrected by shifting each lens in the optical axis direction, the asymmetric distortion aberrations and asymmetric astigmatism which are the optical-axially asymmetrical eccentric aberrations can be corrected by rotating each lens around a rotation axis perpendicular to the optical axis.

Note that the eccentric aberrations may be corrected using a shifting method in which each lens is moved in a direction perpendicular to the optical axis in place of the tilting method in which each lens is rotated around a rotation axis perpendicular to the optical axis.

Next, the aberrations of the optical system should be measured before adjusting it in the above manner. For example, the apparatus disclosed in Kokai H7-54794 can be used for measuring the aberrations. The apparatus used for measuring the aberration is briefly described hereinafter.

FIG. 2 shows an aberration measurement apparatus. Illumination light emitted from a light source 1 is gathered through a first condenser lens 2, and then enters a second condenser lens 3. Provided at the converged light point made by the first condenser lens 2 is a shutter 4 for shielding and transmitting the illumination light. The light passing through the second condenser 3 illuminates a test pattern 5. The test pattern 5 is held by a holder 15 which determines the position of the test pattern 5 in the x and y directions perpendicular to the optical axis z. On the back surface of the test pattern 5, crisscross marks M1,1 through M6,6 are formed so as to guide the light to a plurality of predetermined positions as shown in FIG. 3.

The light passing through the marks Mi,j of the test pattern passes through the reflective-refractive optical system 6 of FIG. 2 whose aberrations are to be measured, and then the image is picked up on an aperture plate 8 held by a stage 7. Provided on the aperture plate 8, as shown in FIG. 4, are an x directional aperture 8a whose width in the x direction is narrow and a y directional aperture 8b whose width in the y direction is narrow. The light passing through these apertures 8a and 8b reaches a photoelectric detector 9 to be photoelectrically converted. A wafer 10 is attached onto the stage 7 via a wafer holder 11. Reflective mirrors 14 are secured at the edges of the stage 7 in the x and y directions, and an interferometer 13 is arranged opposite each reflective mirror 14. Also a gap sensor 12 is provided so as to measure the distance between the reflective-refractive optical system 6 and the aperture plate 8. With this configuration, the position of the stage 7 can be measured in the x, y, and z directions.

As shown in FIGS. 5 and 6, when scanning the aperture plate 8 in the x direction such that the x-directional aperture 8a crosses an image mi,j of any of the test pattern marks Mi,j, the output I from the photoelectric detector 9 first increases and then decreases. Therefore, the x coordinate, xi,j, of the image of the mark Mi,j can be obtained by calculating and averaging the positions x8a, x8b (FIG. 6) that indicate the signals, for example, at 80 percent of the peak value Imax. In the same manner, the y coordinate, yi,j, of the image of the mark Mi,j can be obtained by scanning the aperture 8b in the y direction.

When scanning the defocused position in the x direction by shifting the stage 7 in the z direction, the output of the photoelectric detector 9 changes as shown by dotted lines in FIG. 7 such that the width d8 between the positions x8a and x8b which indicate the signal, for example, at 80 percent of the peak value Imax, narrows, and the width d3 between the positions x3a and x3b which indicate the signals, for example, at 30 percent of the peak Imax, widens. For this reason, finding the position where the difference between both widths (d3 -d8) is the narrowest, by shifting the stage 7 in the z direction, the z coordinate, zi,j of the image of the mark Mi,j can be obtained. The z coordinate of the image of the mark Mi,j may also be obtained by finding the position where the difference (e3-8) between the position X3a indicating the signal at 30 percent of the peak value on the increasing side and the position x8a indicating the signal at 80 percent of the peak value on the same side, becomes the narrowest.

Since all the coordinates, x, y, and z, of the image of a mark Mi,j can be obtained in the above manner, the coordinates, x, y, z, of images of all other marks Mi,j can be found in the same manner to completely obtain the image of the test pattern. For this reason, each aberration can be completely obtained based on these data. By shifting or rotating the lenses L1, L2, L3, and L4 for correcting the aberrations, the reflective-refractive optical system 6 can be adjusted.

As described, the system incorporating the principles of the present invention can correct various aberrations, such as magnification, astigmatism, asymmetric distortion, and asymmetric astigmatism in the reflective-refractive optical system in which the exposure area is relatively large and the N.A. is large.

Various modifications will become possible for those skilled in the art after receiving the teachings of the present disclosure without departing from the scope thereof.

Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
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JPH06331932A * Title not available
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US5969882 *Mar 31, 1998Oct 19, 1999Nikon CorporationCatadioptric optical system
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US6362926Nov 27, 2000Mar 26, 2002Nikon CorporationProjection exposure apparatus and method
US6377338Oct 13, 2000Apr 23, 2002Nikon CorporationExposure apparatus and method
US6451507Aug 18, 1999Sep 17, 2002Nikon CorporationExposure apparatus and method
US6452723Nov 27, 2000Sep 17, 2002Nikon CorporationExposure apparatus and method
US6512641Feb 1, 2002Jan 28, 2003Nikon CorporationProjection exposure apparatus and method
US6627365Sep 18, 2000Sep 30, 2003Nikon CorporationPhotomask and projection exposure apparatus
US6639732Dec 6, 2002Oct 28, 2003Nikon CorporationProjection exposure apparatus and method
US6646797Aug 1, 2002Nov 11, 2003Nikon CorporationExposure apparatus and method
US6707532 *Feb 23, 2001Mar 16, 2004Canon Kabushiki KaishaProjection exposure apparatus
US6707601Apr 21, 2003Mar 16, 2004Nikon CorporationExposure apparatus and method
US6707616Oct 6, 2000Mar 16, 2004Nikon CorporationProjection exposure apparatus, projection exposure method and catadioptric optical system
US6757051Jun 19, 2001Jun 29, 2004Nikon CorporationProjection optical system, manufacturing method thereof, and projection exposure apparatus
US7038761Jan 27, 2004May 2, 2006Canon KkProjection exposure apparatus
US7079314 *Jul 12, 2000Jul 18, 2006Nikon CorporationCatadioptric optical system and exposure apparatus equipped with the same
US7123427 *Jul 20, 2002Oct 17, 2006Carl Zeiss Smt AgObjective, particularly a projection objective for use in semiconductor lithography
US7136220Mar 22, 2004Nov 14, 2006Carl Zeiss Smt AgCatadioptric reduction lens
US7301605Jan 26, 2001Nov 27, 2007Nikon CorporationProjection exposure apparatus and method, catadioptric optical system and manufacturing method of devices
US7317583Aug 21, 2002Jan 8, 2008Asml Holding, N.V.High numerical aperture projection system and method for microlithography
US7319508Jul 24, 2007Jan 15, 2008Nikon CorporationProjection exposure apparatus and method, catadioptric optical system and manufacturing method of devices
Classifications
U.S. Classification359/726, 359/732, 359/730
International ClassificationG03F7/20, H01L21/027, G02B17/08
Cooperative ClassificationG03F7/70275, G02B17/0892, G02B17/08, G03F7/70225
European ClassificationG03F7/70F2, G03F7/70F12, G02B17/08, G02B17/08U
Legal Events
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Apr 29, 2010FPAYFee payment
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Feb 13, 1998ASAssignment
Owner name: NIKON CORPORATION, JAPAN
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:TAKAHASHI, TETSUO;OMURA, YASUHIRO;REEL/FRAME:008973/0541
Effective date: 19970828